1. Field of the Invention
This invention relates to a gas discharge display panel and, more specifically, to an AC-driven, dot-matrix plasma display panel having multiplex wiring for the display electrodes thereof enabling a reduction in the required number of driver circuits, relative to the number of display electrodes, for operating the panel.
2. State of the Prior Art
While various types of flat-panel display devices are known, gas discharge display panels, also known as plasma display panels, have been adopted in a wide number and variety of applications, including use as displays with computer peripheral devices and terminals and with many other types of equipment, such as electronic cash registers, fuel supply indication displays (e.g., dispensed gallons and corresponding purchase cost of fuel) at gasoline stations, time indicators, and the like. Plasma display panels have outstanding features such as high brightness and high contrast ratio as well as long life and suitability for use in relatively large scale displays, contributing to their wide and varied use.
AC-driven plasma display panels are particularly well suited for use in dot-matrix character display devices, in view of the inherent memory function of such panels with respect to data written therein for display. More specifically, in such a panel, each display dot is produced by a gaseous discharge within a discharge cell defined by spatially intersecting electrodes which are covered by corresponding insulating layers and which define therebetween a discharge gas gap. Each discharge, producing a display dot as a result of data written into the display, is effectively memorized in the form of a stored wall charge which is generated by the discharge and established on a corresponding, inner surface of one of the insulating layers of the panel. The wall charge thus produced in a given half-cycle of the applied AC driving voltage is effectively superimposed in additive relationship on the successive half-cycle of the driving voltage applied to that same cell. Thus, if an externally applied voltage of sufficient amplitude is applied to a given gas discharge cell for initiating a discharge, such as a "writing voltage," the gas discharge at that cell thereafter may be sustained by the application of an external voltage of a lower voltage level, since the effective voltage at the cell includes the additive effect of the wall charge potential and the lower amplitude sustaining voltage applied thereto. As a result, a given discharge cell functions in response to the application of a voltage thereto as a bi-state device, taking into account its immediately preceding condition or state. Namely, if a cell is undergoing a discharge (i.e., is "on"), application thereto of a continuous sustaining voltage of lower amplitude than that necessary to initiate the discharge will nevertheless suffice to sustain the discharge in the cell. Conversely, if the cell currently is "off" and thus not sustaining a discharge, application thereto of a sustaining voltage will not produce a discharge; instead, a writing voltage must be applied thereto to initiate a discharge in the cell. This bi-state or bistable characteristic of each cell, as before noted, is a result of the inherent memory function established by the stored wall charge.
The significance of the inherent memory function to the requirements for driving such a panel is that, once data is written into a given discharge cell, there is no need to provide for repetitive or continuous writing of that data into that cell and instead, the memory function will maintain the discharge in the cell, and thus maintain the data. By contrast, in so-called "refresh" mode display panels, data must be continuously written into a cell to maintain same in continuous discharge. Refresh type operation is usually essential to other types of flat-panel display devices, such as DC-driven gas discharge display panels and liquid crystal display panels. Refresh operation introduces other problems in addition to the requirement of continuous addressing of a given cell, including reducing the brightness or contrast ratio which may be achieved by the panel for a given addressing rate, along with decreasing the capacity of the display. By employing the advantages of the inherent memory function, display devices employing AC-driven plasma display panels having large display capacities, such as a 512.times.512 dot matrix display, have been put into practical use, and efforts to develop a panel having a capacity of 1,024.times.1,024 dots or greater continues even today.
Closely aligned with the importance of increasing the dislay capacity of such display panels is the problem of reducing the complexity and cost of the driver circuits for the display. For example, in conventional AC-driven dot-matrix plasma display panels, a driver circuit is provided for each of the X- and Y-electrodes. Thus, for a 512.times.512-dot panel, 1,024 driver circuits are required. As the display capacity of the panel increases, the number of driver circuits concomitantly increases. Thus, reducing the number of driver circuits has become a crucial requirement for achieving cost reduction in dot-matrix display devices, particularly in such devices in which the display panel requires high driving voltages, as typically is true of AC-driven plasma display panels.
Because of the inherent memory capability of AC-driven plasma display panels, as above noted, the individual cells need not be addressed on a continuing basis as in refresh mode operation, but only when data is to be written into a given cell. As a result, the number of driver circuits associated with the X-electrodes, or the number thereof associated with the Y-electrodes--or both--of an AC-driven dot-matrix plasma display panel may be decreased significantly by time-sharing, or multiplexing, the wiring circuits connecting the driver circuits to the electrodes, so long as the electrodes associated with a given discharge cell may be supplied individually with the necessary voltage for writing data into the cell during a writing cycle, following which a sustaining voltage commonly applied to all cells of the panel will sustain, or maintain, discharges in those addressed cells already in discharge (i.e., the "on" cells) while not producing discharges in cells not previously addressed by a writing voltage (i.e., the "off" cells).
A gas discharge panel having capacitively coupled multiplex wiring for the display electrodes is disclosed in the Japanese published patent application Tokukaisho 58-46388, published Mar. 17, 1983. Thus, while the concept of multiplexing the display electrodes of a plasma display panel has been recognized and steps taken to achieve practical implementations of same, there nevertheless has remained a need for improving the configuration of such circuits to achieve improved yields in the fabrication of such circuits and improved reliability and stability in the operation thereof. This need is all the greater, as efforts are made to achieve AC-driven, dot-matrix type plasma display panels of ever greater display capacity.